1. Field of the Invention
The invention relates to optical networks and, more particularly, to the automatic bandwidth adjustment in a passive optical network (PON) with optical network units or ONUs.
2. Description of the Related Art
A passive optical network or PON is an optical network that does not employ, or reduces the use of, active devices such as lasers, regenerators and amplifiers. A PON includes an optical line terminal (OLT), located at the central office (CO) or cable headend, connected to a plurality of optical network units (ONUs). Because of the reduction in the number of active devices, the optical network can improve performance and become more cost-effective in operation and maintenance.
A PON can employ a tree, bus or ring architecture in connecting the single OLT with the ONUs. FIG. 1 is a block diagram generally illustrating a PON with an OLT 11 connected to a plurality of ONUs in a ring structure, including at least ONUs 111, 112, 113, 114 and 115. FIG. 2 is a block diagram generally illustrating a PON with an OLT 21 connected to a plurality of ONUs in a tree architecture, including at least ONUs 211, 212, 213, 214 and 215. FIG. 3 is a block diagram generally illustrating a PON with an OLT 31 connected to a plurality of ONUs in a bus architecture, including at least ONUs 311, 312, 313, 314, 315 and 316. Data travels upstream when the data are transmitted from the ONUs to the OLT. Data travels downstream when the data are transmitted from the OLT to the ONUs. The OLT can also be connected to another optical or non-optical network, e.g., the Internet or an Internet protocol (IP) network. Note that IP is a widely used protocol in the art that specifies the format of packets (also called datagrams in IP network) and the associated addressing scheme. A packet is a piece of a message transmitted over a packet-switching network (such as an IP network) where the packet includes the destination address in addition to the data, and each packet in the network is transmitted individually (which can follow different routes) to its corresponding destination.
As data traffic increases or decreases due to the size and type of data being transmitted in the PON, bandwidth utilization and efficiency may suffer. There is therefore a general need in the art for a PON that allows automatic bandwidth adjustment in optimizing bandwidth usage and thereby improving bandwidth efficiency.
The invention provides an automatic bandwidth adjustment method and system in a passive optical network (PON) comprising an optical line terminal (OLT) connected to a plurality of optical network units (ONUs). A particular embodiment of the method according to the invention comprises the steps of transmitting data between at least one of the ONUs and the OLT, detecting if there is any undelivered data in the data being transmitted, queuing the undelivered data in an undelivered data block (UDB) in an upstream frame of the ONU, informing the OLT of the undelivered data using the undelivered data block (UDB), reading the UDB, adjusting bandwidth of the ONU according to the UDB, informing the ONU whether the PON is busy/unavailable using an unused bandwidth block (UBW), and rejecting a new service transmission request (such as a video on demand (VOD) request) between the ONU and the OLT if the PON is busy or unavailable.
A further embodiment of the method according to the invention comprises the steps of calculating the unused bandwidth (UBW) and informing the ONUs of the UBW, sending an Downstream frame to the ONUs, and determining if an ONU frame (for each of the ONUs) is received at the OLT. If it is determined that an ONU frame is received at the OLT, the UDB is recorded at the OLT, recalculating an automatic bandwidth adjustment beginning (ABAB) and an automatic bandwidth adjustment terminating (ABAT), and calculating a new UBW for each received ONU frame. If an ONU frame is not received at the OLT, a new UBW is calculated for each ONU frame not received at the OLT. The Downstream frame with the recalculated ABAB and ABAT is sent to each of the ONUs.
At the ONUs, the UDB is calculated, and the ONU frames are transmitted to the OLT. At each of the ONUs, it is then determined whether an downstream frame is received. If the Downstream frame is received, each of the ONUs records the recalculated ABAB and ABAT from the received Downstream frame, updates the ABAB and ABAT, checks the UBW for deciding to accept (or not) a new transmission, and calculates a new UDB for each of the transmitted ONU frames. If it is determined that the downstream frame is not received, a new UDB is calculated for each of the transmitted ONU frames. The ONU frames are then transmitted to the OLT with the updated ABAB and ABAT.
With the automatic bandwidth adjustment method and system according to the invention, a PON, through its OLT, can advantageously control the bandwidth for each of the ONUs in the PON and accordingly optimize the overall bandwidth utilization therein.